Microseismic analysis of the geological strata around the bore of fluid injection and production wells is typically effected by the use of seismic sensor assemblies (sondes), mounted downhole in the area of the fluid flow. Usually a number of sondes are mounted in the well at different levels in the bore. Deployment techniques have been developed to allow the sensors to become almost completely mechanically decoupled from the flow induced noise from the tubing.
Systems for permanently installing a sonde against an inner wall of a pipe, such as the casing of a fluid extraction well, are known. Such systems are described in, for example, U.S. Pat. Nos. 5,092,423, 5,181,565, 5,200,581, 5,111,903, 6,289,985, 6,173,804 and 5,318,129.
A sonde may comprise a clamp which permanently or semi-permanently engages with the inner casing of a well. For example, the clamp may be lowered into the well in a retracted state and then once in position expanded to engage with the well casing using a pressure actuated system, which may use external pressure sources or well pressure. Such a clamp is described in EP-A-1 370 891, the contents of which are incorporated herein by reference, which describes C-shaped ring clamps.
These systems may be set using hydraulic pressure derived from the surface using either tubing pressure, annulus pressure or a dedicated hydraulic control line. Disadvantages of these systems are that they are expensive, can suffer from reliability problems and the method of setting the sonde can be driven by the type of well completion.
It is an object of the present invention to provide a sonde securing means and deployment method which overcomes the problems associated with hydraulically actuated systems by providing more simple method of actuation, requiring no surface operational activity.